Method and apparatus for treating work members by the application of high frequency energy

ABSTRACT

A method and apparatus for applying high frequency electrical energy to sheet-like or panel-like work members to develop heat therein for driving off moisture from the work member or for causing the setting of glue therein in which the work member is moved in the direction of its length with longitudinally spaced electrodes in engagement therewith between which high frequency electric current flows through the work piece. Electrical insulating material having high dielectric strength and low loss, and of a noncharring nature, is interposed between the electrodes and the work member, thereby substantially reducing the possibility of arc over along or in the work member and, thus, preventing damage thereto.

United States Patent [191 Slaats et a1.

. METHOD AND APPARATUS FOR TREATING WORK MEMBERS BY THE APPLICATION OF HIGH FREQUENCY ENERGY [75] Inventors: Mathew A. Slaats, Jasper; Arthur W.

Ross, Ferdinand; James E. Blessinger, Jasper, all of Ind.

[73] Assignee: Evansville Veneer & Lumber Co., Evansville, Ind.

[22] Filed: May 8, 1972 [21] App1.No.: 251,126

[52] U.S. Cl 219/10.61, 34/1, 219/1071,

219/1075, 219/1081 [51] Int. Cl. H05b 9/02 [58] Field of Search 219/1061, 10.53,

219/1081, 10.75, 10.77, 10.57, 10.71; 34/1, DIG. 19, 6, 108; 156/273, 274, 275, 380

[451 Sept. 25, 1973 Primary Examiner-.l. V. Truhe Assistant ExaminerB. A. Reynolds Attorney-Melvin A. Crosby [57] ABSTRACT A method and apparatus for applying high frequency electrical energy to sheet-like or panel-like work mem bers to develop heat therein for driving off moisture from the work member or for causing the setting of glue therein in which the work member is moved in the direction of its length with longitudinally spaced electrodes in engagement therewith between which high frequency electric current flows through the work piece. Electrical insulating material having high dielectric strength and low loss, and of a noncharring nature, is interposed between the electrodes and the work member, thereby substantially reducing the possibility of are over along or in the work member and, thus, preventing damage thereto.

7 Claims, 5 Drawing Figures PATENTED SEP25 i975 SHEET 2 BF 2 METIIUI) AND APPARATUS FOR TREATING WOIIK MEMBERS BY THE APPLICATION OF HIGH FREQUENCY ENERGY The present invention relates to a method and apparatus for treating work members with a high frequency electrical energy for the purpose of generating heat within the work member.

High frequency electrical energy has been employed heretofore in respect of developing heat in work members, particularly for drying the work members. High frequency electrical energy employed for this purpose offers the advantages of high speed and relatively compact equipment as opposed to other devices which can be employed for developing heat in a work member, such as heated platens or heated enclosures.

I-Ieretofore, however, there has been a strong tendency for arc overs to occur at the work member, and it can come about because of variations in the composition of the work member of variations in the moisture content or for other reasons which bring about a condition of localized stress in the work member and which can form the starting point for an arc.

When the work member being treated has a finished surface thereon, such arcing over is most undesirable because it can damage the finish of the work piece and require extra finishing operations and may even so seriously damage the work piece that refinishing will not remove the damaged portion. Still further, arcing over can damage the electrodes through which the high frequency energy is impressed on the work piece and, in this case, machine time is lost while the electrode is repaired or replaced.

With the foregoing in mind, a particular object of the present invention is the provision of a method and apparatus for effecting the high frequency treatment of sheet-like or panel-like work members which greatly reduces the possibility of damaging arc overs during the application of the high frequency energy.

Still another object is the provision of a method and apparatus for treating sheet-like or panel-like work members with high frequency electrical energy in order to develop heat in the work member in which the end product can be predicted with accuracy.

Still another object is the provision of a method and apparatus of the nature referred to in which the treatment of the work members, such as for the removal of moisture therefrom, or for the drying of glue lines therein, can be carried out rapidly and efficiently and wherein the apparatus involved is relatively simple in construction and compact.

The foregoing objects as well as still other objects and advantages of the present invention will become more apparent upon reference to the following detailed specification taken in connection with the accompanying drawings in which:

FIG. I is a transverse section through the machine and is indicated by line II on FIG. 2.

FIG. 2 is a longitudinal section through the machine as indicated by line II-II on FIG. 1.

FIG. 3 is a cross section through one of the rollers.

FIG. 4 is a schematic view illustrating the principle of operation of the present invention.

FIG. 5 is a fragmentary sectional view showing a modification.

In FIGS. I and 2, the machine will be seen to comprise a plurality of lower electrodes in the form of rollers 10 and a plurality of upper electrodes in the form of rollers 12, with the rollers spaced apart in each row and with the rows in staggered relation. There may be as many as 15 to 25 rollers in each row, depending upon the nature of the work member to be treated.

The lower rollers 10 are supported on bearings 14 which are, in turn, supported on blocks I6 of electrical insulating material. Blocks 16 are mounted on respective support members 18 extending longitudinally of the frame of the machine and secured to the uprights, or posts, 20 forming part of the main frame of the machine.

Upper rollers 112 are supported on bearings 22 which are fixed to members 26 extending longitudinally of the machine and through which extend the threaded rods 28. Rods 28 are supported by transversely extending members 30 which, at the opposite ends, are interconnected, as by angles 32. The angles 32 at one side of the frame of the machine are pivoted as at 34 to the upper ends of posts 20 and at the other side of the machine are adapted for being secured to the upper ends of the posts as by the pins at 36.

All of the rollers are arranged to rotate in such a direction that the opposed sides of rollers 10 and I2 move in one and the same direction, and at the same surface speed, for transporting sheet-like work members, such as veneer sheets and plywood panels, through the machine. For driving the rollers, there is provided a variable speed motor 38 having speed control means-40 connected thereto. Motor 38 drives via a chain 42 to a sprocket 44 mounted on a shaft 46 which has sprocket 48 mounted thereon at one end. Shaft 46 is made of electrical insulating material, or is divided into opposite end parts joined by a coupling of electrical insulating material. This is done to effect electrical isolation of the two sets of rollers from each other. The supports for the shaft are also electrically insulated from the frame of the machine At the other end, shaft 46 drives through reversing gears 49 to a sprocket 50. Sprocket 48 is connected by a chain to a pair of sprockets 52 that are carried on adjacent ones of the upper rollers 12. These rollers also carry other sprockets 54 which are connected by chains with sprockets 56 on the next adjacent ones of rollers 12. In this manner, all of the rollers 12 are caused to rotate in the same direction and at the same speed.

Similarly, sprocket is connected by a chain with sprockets 58 on a pair of adjacent ones of rollers 10 and additional sprockets 60 mounted on rollers III are interconnected by chains so that all of the rollers It) also rotate in the same'direction, and opposite to the direction of rotation of rollers 12, and at the same pe ripheral speed.

With the rollers rotating in the described manner, a work member, such-as a sheet of veneer, or a plywood panel, introduced into the lefthand side of the machine, as it is viewed in FIG. 2, over table 62, will progress rightwardly through the machine and exit therefrom over table 64.

It will be apparent from FIGS. 1 and 2 that the path taken by the work member, and which path is indicated by the dashed line 66, is undulating so that the work piece is subjected to a certain amount of pressure as it passes through the machine. The exact amount of overlap of the rollers can be adjusted by adjusting the screws 28.

For servicing the machine, the upper part of the frame in which the upper rollers 12 are mounted can be tilted upwardly to expose the path taken by the work members and the lower set of rollers.

Electrical connection can be made to the rollers by the spring blades 15 resting on the roller shafts and connected to busses leading to opposite sides of a generator. A generator is schematically illustrated at 68 in FIG. 4.

FIG. 4 schematically shows the apparatus and will reveal that the upper rollers 12 are all connected to ground while the lower rollers 10, except for the final ones, are connected through respective capacitors C1 to C5 with one side of high frequency generator 68, the other side of which is grounded.

While the first control and best distribution of current is obtained with a capacitor in series with each roll, in practice, only about five capacitors are used and each is connected to a group of adjacent rollers of the lower row with about the final quarter of the lower rollers connected directly to the buss with no interposed capacitor. Thus, in FIG. 4, each roller and each roller 12 represents up to five rollers in the actual machine.

The capacitors C1 to C5 vary in size so as to increase in capacity from C1 to C5 and may range from about 5 picofarods to about 100 picofarods. The reason for this is that a work member introduced from the left side of FIG. 4 at the entrance end of the apparatus will contain considerable moisture and will thus be more highly conductive than the work member will be after it advances toward the right in the apparatus and contains less moisture.

The drying rate can be maintained relatively high with a reduced voltage at the left end of the apparatus, where the work member is quite moist, whereas, toward the right end of the apparatus, where the work member exits, a substantial amount of the moisture has been removed from the work member and a higher voltage is required to maintain the same drying rate.

The difference in conductivity of the work member at the wet end of the apparatus from the conductivity thereof at the dry end of the apparatus is substantial, and the ratio of these values may be as much as 100 to 1. Since the rate of moisture removal is proportional to the square of the voltage drop in the work member, it will be evident that the voltage requirements along the path of travel of the work member vary substantially with the highest voltage being required at the dry end of the apparatus. The capacitors referred to form an inexpensive low loss device for obtaining the required variation in applied voltage and current flow.

A furthercontrol on the current distribution can be effected by varying the spacing between the electrodes in the direction of the length of the work member. In this case, the rollers at the wet end of the apparatus would be farther apart than those at the dry end. Variation in the spacing of the electrodes, or rollers, together with the aforementioned capacitors in series with the rollers, makes for any desired control of current flow in the work member.

Thus, by progressively increasing the size of the capacitors from C1 to C5, the load can be distributed along the length of the machine and a substantially continuous drying rate from one end of the machine to the other can be maintained. Near the exit end of the apparatus, as shown in FIG. 4, no capacitors are employed and full generator voltage is applied to the electrodes.

The current flow in the work member is also illustrated in FIG. 4, by the dashed lines 14, which will be seen to be substantially in the direction of the length of the work member, thereby efficiently treating the work member.

A particular feature of the present invention is found in the construction of the rollers and which are shown in detail in FIG. 3. The rollers comprise a conductive central part 70, steel, for example, although other conductive materials of suitable structural strength are satisfactory. The roller can either be solid or hollow as may be desired and, in most cases, will be hollow, for reasons of weight and economy.

According to the present invention, a layer 72 is provided on the outer surface of the rollers, and this layer is characterized in being an electrical insulating material having high dielectric strength and low dielectric loss and which will not char when an arc-over, or arcthrough, occurs. Among such materials are ceramics, glass, and silicone rubber, although other materials will suggest themselves to those skilled in the art.

The advantage of the outer layer on the rollers is that the tendency for the machine to arc over between adjacent rollers is greatly reduced. Such a tendency can result from current concentration and an attendant heat build up. This reduction in the tendency to arc over comes about, in particular, because of the insulation of the metal of the rollers from the work member engaged thereby and which tends to prevent current concentration at the work member surface, because a gap is introduced at each end of the path of current flow from roller to roller and across which gap the larger portion of the voltage drop between the rollers occurs.

The covers on the rollers thus serve as a current limiting arrangement and, in combination with capacitors in series with the rollers, distributes the current in the work member. The voltage level at the bus, or busses, of the apparatus is maintained, and there is no tendency for all of the power supplied to drain through a path of lowest resistance.

Inasmuch as the material covering the rollers is noncharring in nature, even though there is a strike through of current, no loss of insulating or dielectric value of the roll ever occurs and operation of the apparatus can continue without shutting it down to clean the rollers or to replace a roller or to repair the cover thereof.

Since the coating material on the rollers is characterized in low dielectric loss, there is substantially no load on the system due to the presence of the covermaterial on the rolls. No substantially greater amount of power is consumed than would be consumed under other circumstances, although somewhat higher voltages may be required.

In the drying of veneer, which may range from about 1/85 of an inch thick up to about one-fourth of an inch thick, the generator 68 may develop about 5,000 volts at from about 1 to about megacycles per second. Veneer entering the machine may have a very high moisture content, and the moisture content may be distributed irregularly therein, but the veneer will dry uniformly in passing through the machine down to a uniformly distributed content of about 5 to 10 per cent moisture and which is the desired amount of moisture for veneer to carry.

The Staggered arrangement of the rollers insures that the electrical current passing from one roller to another will be in the direction of the length of the veneer and will, therefore, be utilized efficiently in heating the veneer and driving moisture therefrom.

The high frequency current distributes over the cross section of the work member and is greatest in the moist regions and is, thus, highly efficient for heating the work member completely through. A distinct advantage in speed and uniformity of drying is obtained over arrangements wherein hot air is passed over the work piece or wherein the work piece is pressed between hot platens.

While the drying of veneer has been referred to above, the drying of glue in plywood panels can also be carried out in the apparatus of the present invention. In the case of drying glue in plywood that has been laid up from sheets of veneer, the glue is dried by not much, if any, moisture will be driven from the work member.

ln either case, the temperatures of the work member will not rise above a certain temperature in the machine, but will strike a balance between the heat generated therein and the heat loss therefrom. The results obtained by passing a work member through the machine is, accordingly, predictable and overtreatment is avoided.

In the treating of at least some plywoods, cover sheets in the form of veneer are applied to opposite sides of a prefabricated core and the glue joining the veneer to the core is to be dried. In such a case, a modification as schematically illustrated in FIG. 5 may be employed.

In FIG. 5, 80 is the prefabricated core and 82 and 84 are veneer sheets applied to opposite faces of the core with glue therebetween. Since the core is prefabricated, no energy need be supplied thereto so a plurality of pairs of electrodes between which current pass are on the same side of the panel. I I The rollers 86 and 88, which engage the panel on opposite sides, are spring urged toward each other by spring means 90. The rollers are driven in opposite directions at the same peripheral speed and advance the panel toward the right and also press the veneer sheets against the core of the panel.

Rollers 86 and 88 are grounded and arranged in trailing relation thereto are the hot electrodes 92 and 94 which may merely drag on the panel. Electrode 92 may rest by its own weight on the panel while electrode 94 may be pressed toward the panel by a spring 96.

Each of the electrodes, namely, each of the rollers and each of the drags are provided with a coating of the nature referred to above.

There would, of course, be as many sets of rollers and drags as necessary to treat the work member and the drags would be connected to the supply via capacitors as previously described. Also, the spacing between the rollers and the drags pertaining thereto could be varied to provide for current control as previously described.

-In respect of the prefabricated core, the individual layers thereof could be dried in a machine according to the present invention and the core laid up therefrom also dried in the same manner before the application of the outer veneer layers thereto.

When panels are treated to dry glue joints and there is little, or no, moisture given off from the work member, and the electrical insulating material can be interposed between the panel and the rollers in the form of a sheet which moves with the panels but when driving moisture from a veneer sheet, or a panel, the work member must be exposed and the insulating material will be mounted directly on the electrodes.

Modifications may be made within the scope of the appended claims.

What is claimed is:

ll. In an apparatus for treating a flexible sheet-like work member by the application thereto of high frequency electrical energy, said apparatus comprising a frame with an undulating path extending through the frame from an entrance end to an exit end and adapted for the movement therealong of sheet-like work members, high frequency generator means, a plurality of first and second electrode means in said frame in distributed relation along said path, means connecting said first electrode means to one side of said generator means and said second electrode means to the other side of said generator means, said first and second electrode means being adapted to engage opposite surfaces a sheet-like work member disposed on said path and to guide the work member along said path, said first and second electrode means being disposed in spaced alternating relation along said path for the transfer of energy between adjacent ones of said first and second electrode means and through the work member in the direction of the length thereof as said work member moves relative to said electrode means along said path, low dielectric loss electrical insulating material encapsulating each said electrode means, capacitor means interposed between at least some of said electrode means and the respective side of said generator and increasing in capacitance from the entrance end of said frame toward the exit end thereof, and means for advancing a work member along said path from the entrance end of the frame to the exit end thereof.

2. An apparatus according to claim 1 in which said first and second electrode means comprise rollers and are disposed on respective upper and lower rows in said frame with the rollers of each row in spaced coplanar parallel relation on a respective side of said path, said rollers of said upper row thereof being arranged in alternating staggered relation to said rollers of said lower row thereof, said means for advancing a work member along said path comprising means for driving said rollers of said lower row thereof in one direction of rotation and said rollers of the upper row thereof in the opposite direction of rotation whereby a sheet-like work member introduced endwise between said rows of rollers at the entrance end of the frame will be conveyed in the direction of the length thereof between the rollers of the said upper and lower rows thereof to the exit end of the machine, each roller having a metallic core, and said electrical insulating material comprising a coating of substantially uniform radial dimension on each roller and extending about the entire peripheral and axial extent of the respective roller.

3. An apparatus according to claim 2 in which said frame includes a stationary lower part in which the rollers of said lower row are rotatably mounted and an upper frame part in which said rollers of the upper row are rotatably mounted, and means tiltably connecting one side of said upper frame part to the corresponding side of said lower frame part for tilting of the upper frame part on the lower frame part to expose the sides of said rollerswhich face the said path along which a work member moves through said frame.

4. An apparatus according to claim 3 in which said upper frame part includes means adjustably supporting said upper row of rollers therein for movement of the upper row of rollers therein toward and away from the plane of said rollers of the lower row thereof.

5. An apparatus according to claim 2 which includes means for adjusting the rollers of at least one of said rows toward and away from the plane of the other row of rollers.

6. An apparatus according to claim 1 in which said first electrode means comprises upper and lower rollers arranged in a plurality of opposed pairs and the rollers of each pair being biased toward each other to engage opposite faces of a sheet-like work member disposed on said path, each said pair of rollers being connected to the same side of said generator means, said second electrode means comprising a pair of electrodes arranged in trailing relation to each said pair of rollers and also engaging opposite faces ofa work member disposed on said path and being connected to the opposite side of said generator means, and said means for advancing a work member along said path comprising means for driving at least said rollers to convey a sheetlike work member along said path and through said frame from the entrance end thereof to the exit end thereof.

7. An apparatus according to claim 1 in which said electrode means are spaced farther apart at the entrance end of the frame than at the exit end thereof. 

1. In an apparatus for treating a flexible sheet-like work member by the application thereto of high frequency electrical energy, said apparatus comprising a frame with an undulating path extending through the frame from an entrance end to an exit end and adapted for the movement therealong of sheet-like work members, high frequency generator means, a plurality of first and second electrode means in said frame in distributed relation along said path, means connecting said first electrode means to one side of said generator means and said second electrode means to the other side of said generator means, said first and second electrode means being adapted to engage opposite surfaces a sheet-like work member disposed on said path and to guide the work member along said path, said first and second electrode means being disposed in spaced alternating relation along said path for the transfer of energy between adjacent ones of said first and second electrode means and through the work member in the direction of the length thereof as said work member moves relative to Said electrode means along said path, low dielectric loss electrical insulating material encapsulating each said electrode means, capacitor means interposed between at least some of said electrode means and the respective side of said generator and increasing in capacitance from the entrance end of said frame toward the exit end thereof, and means for advancing a work member along said path from the entrance end of the frame to the exit end thereof.
 2. An apparatus according to claim 1 in which said first and second electrode means comprise rollers and are disposed on respective upper and lower rows in said frame with the rollers of each row in spaced coplanar parallel relation on a respective side of said path, said rollers of said upper row thereof being arranged in alternating staggered relation to said rollers of said lower row thereof, said means for advancing a work member along said path comprising means for driving said rollers of said lower row thereof in one direction of rotation and said rollers of the upper row thereof in the opposite direction of rotation whereby a sheet-like work member introduced endwise between said rows of rollers at the entrance end of the frame will be conveyed in the direction of the length thereof between the rollers of the said upper and lower rows thereof to the exit end of the machine, each roller having a metallic core, and said electrical insulating material comprising a coating of substantially uniform radial dimension on each roller and extending about the entire peripheral and axial extent of the respective roller.
 3. An apparatus according to claim 2 in which said frame includes a stationary lower part in which the rollers of said lower row are rotatably mounted and an upper frame part in which said rollers of the upper row are rotatably mounted, and means tiltably connecting one side of said upper frame part to the corresponding side of said lower frame part for tilting of the upper frame part on the lower frame part to expose the sides of said rollers which face the said path along which a work member moves through said frame.
 4. An apparatus according to claim 3 in which said upper frame part includes means adjustably supporting said upper row of rollers therein for movement of the upper row of rollers therein toward and away from the plane of said rollers of the lower row thereof.
 5. An apparatus according to claim 2 which includes means for adjusting the rollers of at least one of said rows toward and away from the plane of the other row of rollers.
 6. An apparatus according to claim 1 in which said first electrode means comprises upper and lower rollers arranged in a plurality of opposed pairs and the rollers of each pair being biased toward each other to engage opposite faces of a sheet-like work member disposed on said path, each said pair of rollers being connected to the same side of said generator means, said second electrode means comprising a pair of electrodes arranged in trailing relation to each said pair of rollers and also engaging opposite faces of a work member disposed on said path and being connected to the opposite side of said generator means, and said means for advancing a work member along said path comprising means for driving at least said rollers to convey a sheet-like work member along said path and through said frame from the entrance end thereof to the exit end thereof.
 7. An apparatus according to claim 1 in which said electrode means are spaced farther apart at the entrance end of the frame than at the exit end thereof. 